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Diffstat (limited to 'Lessons/Lesson_25/README.md')
| -rw-r--r-- | Lessons/Lesson_25/README.md | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/Lessons/Lesson_25/README.md b/Lessons/Lesson_25/README.md index 15b0b85..ccbcc90 100644 --- a/Lessons/Lesson_25/README.md +++ b/Lessons/Lesson_25/README.md @@ -144,6 +144,25 @@ PcdDynamicInt32=0xCAFECAFE PcdDynamicInt32=0xBEEFBEEF ``` +As we don't always use our application as a part of Ovmf package it would be better to guard the `PcdDynamicInt32` access for cases when local tokan is unassigned. + +We can do it with a help of a `PcdToken` macro: +``` +#define PcdToken(TokenName) _PCD_TOKEN_##TokenName +``` + +Code usage as simple as this: +``` +if (PcdToken(PcdDynamicInt32)) { + Print(L"PcdDynamicInt32=0x%x\n", PcdGet32(PcdDynamicInt32)); + PcdSet32S(PcdDynamicInt32, 0xBEEFBEEF); + Print(L"PcdDynamicInt32=0x%x\n", PcdGet32(PcdDynamicInt32)); +} else { + Print(L"PcdDynamicInt32 token is unassigned\n"); +} +``` +At least now if you accidently copy `Build/UefiLessonsPkg/RELEASE_GCC5/X64/PCDLesson.efi` instead of `Build/OvmfX64/RELEASE_GCC5/X64/PCDLesson.efi` the application won't break the OVMF. + # Dynamic Ex PCD Suppose we already have the necessary PCD in the PCD Database. And we want to access it via application from the UEFI Shell. |